Zoological Journal of the Linnean Society, 62: 381-400. With 8 plates and 5 figures
April 1 9 7 8
A new sniall theropod dinosaur from the
Judith River Formation (Campanian) of Alberta
Canada
HANS-DIETER SUES*
Department of Geology, The University of Alberta,
Edmonton, Alberta, Canada
Accepted f o r publication September 1976
A new small theropod dinosaur, documented by an incomplete skeleton and three frontals, is
described from the Judith River Formation (Upper Cretaceous: Campanian) of south-central
Alberta.
I t is distinguished from both Stenonychosaurus and Dromaeosaurus by the structure of the
frontal and by the marginal dentition.
I t resembles Stenonychosaurus in the structure of the frontal and the Dromaeosauridae in
the shape of the endocranial cavity and other skeletal features.
The material is referred to a new genus and species of the Dromaeosauridae.
K E Y WORDS:
-
Saurischia
-
Dromaeosauridae ~ - J u d i t hRiver Formation
-
Alberta.
CONTENTS
Introduction
. . . .
. . . .
Systematics
Description
. . . .
Skull
. . . .
Postcranial skeleton
Taxonomic discussion
.
. .
Acknowledge men ts
. . . .
References
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381
382
383
383
391
395
400
400
INTRODUCTION
In 1974, Mrs Victor Vanderloh of Cessford, Alberta, discovered associated
remains of the skull and postcranial skeleton of a small theropod dinosaur in
the Dinosaur Provincial Park, north-east of Patricia, south-central Alberta.
This discovery was of considerable interest, as associated remains of small
theropods are very rare in the classical collecting area of the Judith River
Formation (Oldman Formation of authors) of south-central Alberta. The
material mainly consists of teeth and isolated elements of the appendicular
skeleton, especially phalanges and unguals.
Study of the new find revealed that it is not, as informally reported by the
Provincial Museum and Archives of Alberta at the time of discovery, a
* Present address: Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts
02138, U.S.A.
381
382
H.-D. SUES
specimen of Stenonychosuurus inequalis Sternberg, 1932, but rather it
represents a new taxon different from previously described Judithian
theropods.
Furthermore, the new find fulfills the hope expressed by Russell (1969:
612) that some of the isolated bones in the older collections from the Judith
River Formation may become determinable once more complete material
becomes available. I t can be shown that three frontals listed by Russell as
indeterminate are conspecific with the new material described herein.
The following abbreviations of institutional names were used in the text to
identify the place of storage for specimens under discussion, preceding
specimen numbers: AMNH, American Museum of Natural History, New York;
NMC, National Museum of Natural Sciences, Ottawa; PMAA P,
Palaeontological Collections, Provincial Museum and Archives of Alberta,
Edmonton; UA, The University of Alberta, Edmonton; YPM, Peabody Museum
of Natural History, Yale University, New Haven.
SYSTEMATICS
Class Reptilia
Order Saurischia
Suborder Theropoda
Family Dromaeosauridae
Saurornitholestes gen. nov.
Etymology. From oalipoc (Greek): lizard, 6 p v ~(Greek): bird, hqm-fiq
(Greek): robber; in reference to its similarity to the saurornithoididae and its
carnivorous mode of life.
Type species. Saurornitholestes langstoni, new species.
Distribution. Judithian (Campanian), Alberta.
Diagnosis. Same as for the type and only species, given below.
Saurornitholestes langstoni sp. nov.
Etymology. For Dr Wann Langston, Jr., now of Austin, Texas, in recognition
of his contributions to Canadian vertebrate palaeontology and his personal
interest and generous support of the author’s work.
Holotype. PMAA P74.10.5, associated remains of an incomplete skeleton,
including both frontals, left ectopterygoid, left quadrate, two teeth, two
vertebrae, gastralia, fragments of thoracic ribs, a metactirpal, several phalanges
and all unguals of the left manus, three isolated prezygapophyses and a number
of very fragmentary bones, which are cndeterminable at present.
Horizon and type locality. Judith River Formation (Campanian), Dinosaur
Provincial Park, south-central Alberta. The site is located in lsd. 13, section 27,
township 21, range 12 west of the Fourth Meridian. The specimen was
collected from a buff sandstone, exposed approximately 180 to 210 m above
the floor of the valley.
Hypodigm. The holotype and three frontals, listed by Russell (1969: 612) as
indeterminate at that time: UA 5283, posterior part of a left frontal. From a
site 1.5 miles S. E. of the Dinosaur Provincial Park Headquarters, in lsd. 14,
THEROPOD DINOSAUR FROM ALBERTA
383
section 32, township 20, range 11 west of the Fourth Meridian. NMC 12343
and NMC 12354, incomplete left frontals. Both were found in the Dinosaur
Provincial Park but no precise locality data have been recorded; one specimen
was collected on the South side of the Red Deer River opposite Happy Jack’s
ranch, section 2, township 21, range 11 west of the Fourth Meridian.
Diagnosis. Very small, lightly built theropod. Frontal triangular, not basined
between the median suture and the orbital rim. Posterior part of the frontal
well-rounded and slightly inflated, without frontoparietal crest. Lateral walls of
the anterior part of the endocranial cavity flaring laterally. Ectopterygoid
complex, pocketed ventrally. Teeth with well-developed denticles (24-26 per
5 mm) on posterior carinae and tiny denticles (c. 3 5 per 5 mm) on anterior
carinae.
DESCRIPTION
Skidl
(Figs 1 to 3 , 4 B ; Plates 1 to 3 , 4 (fig. A))
The cranial material of Suurornitholestes lungstoni consists of the frontals,
the left ectopterygoid, the left quadrate and two teeth.
Plate 1. Saurornitholestes langstoni, sp. nov., holotype. Stereophotographs of the frontals: A,
dorsal view; B, ventral view.
H.-D. SUES
384
I
cm
B
Figure 1. Saurornitholestes Inngsroni, sp. nov. Holotype, frontal region: A, dorsal view; B,
ventral view.
Frontal. The frontal is triangular and relatively longer than wide in
comparison with the corresponding element in Stenonychosaurus. Behind the
orbit i t makes an abrupt lateral turn to form the pedunculate base for the
postorbital. The frontal is smaller than that of the smallest specimen of
Stenonychosaurus (AMNH 6174) studied: It measures 54.5 mm along the
midline of the skull dorsally, compared with 72.5 mm in AMNH 6174. The
frontal of P74.10.5 measures 32.0 mm in a straight line from the midline suture
to the tip of the postorbital process (52.2 mm in AMNH 6174). The
interorbital width is large. The frontals are joined for their entire length along a
median suture. In contrast to Stenonychosaurus and Dromaeosaurus, they are
not basined between the median suture and the orbital rims. Along the anterior
edge of the frontal, surfaces for articulation with nasal, prefrontal and lacrimal
are exposed. Two narrow, U-shaped facets on either side of the median suture
can be ascribed to the overlap of the nasals. The surfaces for the overlap of
THEROPOD DINOSAUR FROM ALBERTA
385
A2
I
-O
A
cm
B
I
0
cm
Figure 2. Saurornitholestes langstoni, sp. nov. Holotype: A, size comparison between the
frontal of Stenonychosaums (AMNH 6174; A l ) and the frontal of Sauromitholestes (holotype;
A2); B, quadrate in ventral view.
prefrontal and lacrimal cannot be distinguished with certainty. The sutural
contact between the frontal and the parietal is very irregular and closely
interdigitating, thus preventing any mobility in thi, region of the skull. The
orbital margins are roughened. The orbit is large and spherical. The posterior
margin of the frontal lacks a frontoparietal crest but is well-rounded and
smooth and appears to be slightly inflated. The anterodorsal limit of the
supratemporal fenestra is indicated by a weakly developed ridge (especially well
visible in UA 5283, which belongs to a slightly larger individual) sigmoidally
curving posteromedially from the posterodorsal corner of the orbit toward the
cranial midline, disappearing prior t o meeting the median suture.
386
tl.-D. S U E S
Plate 2. Sourornitholestes langstoni, sp. nov. Stereophotographs of an incomplete left frontal
(UA 5283), showing details of the posterior region: A, dorsal view; B, ventral view.
On the ventral surface of the frontal the impressions of the olfactory bulbs
and cerebral hemispheres are visible. Relative t o the impressions on a frontal of
Dromaemaurus (NMC 12349), the olfactory bulbs are smaller and the cerebral
hemispheres are larger. The endocranial cavity is relatively larger than in
Stenonychosaurus. The lateral walls of the anterior part of the endocranial
cavity flare out and show sharply defined ventral edges.
Quadrate. An incomplete left quadrate closely resembles the corresponding
element of Dromaeosaurus (Colbert & Russell, 1969: fig. 9).
A large part of the mandibular articulation and the distal part of the
ascending process are preserved. The mandibular articulation is broad and
transversely oriented. Lateral and medial condyles are traversed by an obliquely
and anteromedially extending groove. The ascending process is too
incompletely preserved to warrant description.
Ectoptervgoid. A single incomplete element, triradiate and closely
resembling the ectopterygoid of Deinonychus (Ostrom, 1969: fig. 1 3 and cast
of YPM 5210) and of Drornaeosaurtis (Colbert & Russell, 1969: fig. l o ) , is
interpreted as a left ectopterygoid. I t has a stout, hook-shaped lateral process
curving posteriorly and lateroventrally, abutting against the inner surface of the
jugal in life. A second, more robust process extends posteroventrally but much
of it is broken off. It probably formed the ectopterygoid flange, as in
Deinonychus (YPM 5210). The ventral surface of this process shows a deeply
excavated pocket of unknown function, as in Deinonychus, Dromaeosaurus,
Albertosaurus (Ostrom, 1969: 27), Daspletosaurus (Russell, 1970: fig. 9),
THEROPOD DINOSAUR FROM ALBERTA
A
387
B
0
I
0
I
I
I
crn
cm
C
-
0
I
1
rnm
Figure 3. Saurornitholestes longstoni sp. nov. Holotype, ectopterygoid: A, dorsal view; B,
ventral view: C, detail of the dorsal surface of the pterygoid process.
H.-D. SUES
388
Table 1.Distal transverse widths of the phalanges
and the metacarpal ?
Digit
Digit
Digit
Digit
Digit
I, 1
11, 2
111, mtc. ?
Ill, 1
Ill, 3
9 . 8 mm
9.5 mm
6.6 mm
7.7 mm
8.9 mm
Table 2. Dimensions of the ungual phalanges
Phalanx
1, 2
11, 3
111, 4
Length along outer
curve (mm)
-
48.5
36.6
Height of facet
(mm)
Proximal transverse
width (mm)
13.6
13.0
11.2
6.3
6.2
5.3
Tyrannosaurus (Osborn, 1912: fig. 6), and Allosaurzis (Gstrom, 1969: 27),
being relatively much smaller in the latter four genera. The flattened pterygoid
process, the dorsal surface of which is marked by a conspicuous oval
depression, extends medially from the base of the ectopterygoid and jugal
processes. The depression on the pterygoid process is subdivided by a ridge.
The left pit is oval and shows a small foramen anteriorly and two smaller ones
posteriorly. The right pit is wedge-shaped and houses three foramina: a small
anterior one, a small lateral one and a large posterior one, which opens to a
canal continuing posteriorly into the large ventral pocket of the ectopterygoid
flange. The depression corresponds to the “small, oval pit, marking the dorsal
Figure 4. A. Stenonychosaurus inequalis: ventral view of the endocranial cavity. B .
Suurornirholestes langstoni: ventral view of the endocranial cavity (not to scale).
1 H E R O P O D DINOSAUR FROM ALBERTA
389
Plate 3. Suurornirhofesres fungstoni, sp. nov. Stereophotographs of’ two referred frontals (NMC
1 2 3 4 3 and NMC 12354): A, dorsal view; B, ventral view. (In all photographs: upper row: NMC
12354, bottom row: NMC 12343.)
surface of this process [ectopterygoid process-HDS] at its junction with the
jugal process” mentioned by Ostrom (1969: 27), although it is not shown in
the illustration of the ectopterygoid in that paper (Ostrom, 1969: fig. 1 3 ) .
Personal examination of a cast of the right ectopterygoid (YPM 5210) of
D e i i ~ o ~ z ~ shows
~ c h s a relatively conspicuous pit in the same position as on the
ectopterygoid of Suurornitholestes. Ostrom (1969: 27) suggested that this pit
might be related to the origin of the M . pterllgoicieus dorsalis.
21
3 90
H:D.
SUES
Plate 4. Sauromitholestes langstoni, sp. nov., holotype. A. Stereophotographs of a tooth. B.
Stereophotographs of phalanges and a ?metacarpal of the manus: 1 , phalanx 1 , digit 1 1 1 ; 2,
?metacarpal, digit I l l ; 3, phalanx 2, digit 11; 4, phalanx 1 , digit I ; 5 , phalanx 3, digit Ill.
Teeth. Two isolated teeth are present among the material. They are small,
sharply tapered, laterally compressed and distinctly recurved. The roots of the
teeth are parallel-sided. One tooth shows a pit in its base, produced by basal
resorption during the process of replacement. A distinctive feature of the teeth
is the extreme size disparity between the serrations on the anterior and
posterior carinae. The posterior carinae show well-developed denticles (24-26
per 5 mm), whereas the anterior carina only shows very small denticles (c. 3 5
per 5 mm), which are three to four times lower than those on the posterior
carina and give the anterior carina a fluted appearance. The serrations on the
THEKOPOD DINOSAUR FKOM ALHLKTA
39 1
anterior carina only extend along about 70% of the height of the crown. The
very tip of the tooth lacks serrations on either side. The crown of the tooth is
slightly asymmetrical, i x . , a plane passing through the anterior and posterior
denticles divides the tooth unequally.
Troodon .formoms (based on but a single tooth) (L. S. Kussell, 1948: figs
1-3) differs in having subequal anterior and posterior denticles and only having
7-8 serrations per 5 mm.
In Suurornitizoides junior most teeth show denticles only along the posterior
edge (Barsbold, 1974: fig. 6); a few teeth may have denticles on the anterior
carina but then only at the base of the crown (Barsbold, 1974: 20). Although
the teeth are poorly preserved in Suttrornitlioides mongoliensis (AMNH 65 16),
denticles appear to be limited to the posterior edge. The same condition is
found in several teeth described from the Lance Formation by Estes (1964:
142, 143) as cf. Satirorriithoides sp. and Puronychodon lucustris. The teeth of
cf. Suztrornithoides sp. are characterized by a deeply denticulated posterior
carina with 7 t o 12 very large serrations (Estes, 1964: fig. 69a); such teeth are
now also known from the Judith River Formation of Alberta (Sues, in
progress). The teeth referred to Purotij'cliodotz lucustris are described as having
finely denticulated posterior and smooth leading carinae (Estes, 1964: 143).
Suurornithoides mongoliensis has 12 serrations per 5 mm, as have the maxillary
teeth of Suurornithoides junior, whereas the dentary teeth of the latter species
have 15 to 1 7 per 5 mm (data for Suzirornithoides jztrzior from Barsbold, 1974:
20).
The teeth of Velocirupror mongoliepisis (AMNH 6515) differ in the number
of denticles (38 to 40 denticles per 5 mm on anterior carinae, 25 to 26 on
posterior; Colbert & Russell, '1969: 40) and in having better developed anterior
denticles.
The teeth of Dromueosaztrt~sulbertensis (AMNH 5 3 56) differ in having
well-developed anterior serrations, the number of denticles (1 6 per 5 mm on
both carinae) and (in the anterior part of the jaw) by the medial displacement
of the anterior carinae near the base of the crown.
The teeth of Deinonyclius antirrhoptis (see Ostrom, 1969) differ in the
number of denticles (30-31 denticles per 5 mm on anterior carinae, 16-18 on
the posterior carinae) and in having better developed anterior denticles (which
are half as large as those on the posterior carinae).
It is evident from the comparisons that the teeth of Saurornitholestes more
closely resemble the teeth of the Dromaeosauridae than those of the
Saurornithoididae.
Postcraniul skeleton
(Fig. 4; Plates 4 (fig. B), 5 and 6)
Vertebrae. A well-preserved centrum with a large eart of the neural arch
probably belongs to a posterior dorsal vertebra. The centrum is slightly
platycoelous and the anterior and posterior surfaces for intercentral
articulation are almost parallel. A ventral keel is absent. The centrum is
constricted at mid-length and the ventral and lateral surfaces are strongly
concave in longitudinal direction. I t is 18 mm long, 23 mm high and 25 mm
wide posteriorly. The lateral surfaces of the centrum show deep pleurocoels
392
FI-D. SUES
Plate 5 . Suurornitholestes lungstoni, sp. nov., holotype. Stereophotographs of the unguals of the
left manus: A, phalanx 3, digit 11; B, upper row: phalanx 2, digit 1; bottom row: phalanx 4,
digit 111.
parallel to the suture of the neural arach. Within the pleurocoels a large anterior
and a small posterior opening can be distinguished. No parapophyses are visible.
The neural arch is incomplete; the left half and part of the spine are broken off.
The diapophysis is very short and the arch is excavated. The edges of the neural
spine show very rugose furrows, probably areas of attachment for interspinous
ligaments (Ostrom, 1969: 57).
Three isolated prezygapophyses are present among the material. They are
subcircular, of moderate size and appear t o be very similar to those of the
anterior dorsal vertebrae of Deinonychus (Ostrom, 1969: fig. 33).
THEROPOD DINOSAUR FROM ALBERTA
Plate 6. Suurornirholesres lungstoni, sp. nov., holotype. A. Gastralia: 1-2, lateral segments of
gastralia “ribs”: 3, medial segment of a gastralia “rib”. B. Fragments of thoracic ribs: 1, head of
a mid-dorsal rib: 2, head of an anterior dorsal rib: 3, shaft fragment. C. Posterior dorsal
vertebra: 1 , right side: 2, anterior view. D. Centrum of a ?first ?dorsal vertebra: 1, left side; 2 ,
anterior view.
393
394
14.-D. SUES
An incomplete centrum shows roughly triangular surfaces for intercentral
articulation. The posterior surface is incompletely preserved dorsally but
appears to be slightly higher than the anterior one. The centrum is constricted
at mid-length. A large, subcircular pleurocoel (quite different from the
pleurocoels on vertebrae of Deinonychus (see Ostrom, 1969)) is situated near
the posterior end of the lateral surface of the centrum. A ventral keel is
present. The centrum is 18 mm long, 1 3 mm high anteriorly and its maximum
width anteriorly is c. 1 3 mm. There is some resemblance to the first dorsal
(“cervicodorsal”) vertebra of Deirzonychus (Ostrom, 1969: 5 3) in the presence
of a ventral keel and the shape of the anterior surface of the centrum, but the
specimen under discussion differs with regard to the shape and position of the
pleurocoel and in being relatively longer than high.
Ribs. Ribs are represented by two incomplete rib-heads and several shaft
fragments. In the more completely preserved rib-head the capitular process
seems to be longer than the tubercular process but the latter is incomplete. The
surface of the capitulum is oval, convex and smooth. The surface of the
tubercular process is situated above and is widely separated (c. 20 mm) from
that of the capitular process. The separation of the capitular and tubercular
surfaces suggests that the rib-head probably belongs to a more anterior rib. I t
differs from the heads of the dorsal ribs of Deinonychus described by Ostrom
(1969) in that the tubercular process is directed posteriorly. In the other
rib-head part of the capitular process is broken off but the tubercular process is
preserved: The tuberculum is situated posteriorly to the capitulum and the
tubercular process is only very small. The adjacent, expanded proximal part of
the rib-shaft is an extremely thin lamina of bone. The marked similarity
between the fragment and a mid-dorsal rib (YPM 5249) of Deinonychiis
suggests reference of the rib-head t o a mid-dorsal rib.
Gustruliu. An almost complete, broadly curved rib-like bone and a large part
of another probably represent segments of gastralia “ribs”. They are slender
rods, tapering toward both ends and oval in transverse section at mid-length. A
similar element in Stenonychosuurus (Russell, 1969: fig. 8) is more robust and
shows much stronger curvature.
One incomplete, somewhat flattened rod with an expanded articular surface
at the preserved end shows reseniblance to a medial segment of a gastralia rib of
Deinonychus illustrated by Ostrom (1969: fig. 52C,D).
Munus. Remains of all three digits of the left manus are available.
Identifications were made on the basis of comparison with excellent casts of
the elements of the left manus of Deinonychus (YPM 5206 and YPM 5215),
generously forwarded by Dr J. H. Ostrom. The three unguals (one of them
lacking the distal extremity) clearly belong to the manus, as shown by the
position of the proximal articular facet. They very closely resemble those of
the manus of Deinonychus. The unguals are large, strongly curved, laterally
compressed and stoutly constructed. The articular facets are well-defined and
ridged. A large flexor tubercle (for attachment of strong flexor muscles)
projects ventrally well below the inferior border of the articular facet and
shows a rugose surface. Laterally the unguals show a deep groove extending
from the base of the proximal articular facet t o the tapering distal extremity on
each side. The ungual phalanges 3 of digit I1 and 4 of digit I11 appear to be
subequal in size.
THEKOPOD DINOSAUR FKOM ALBERTA
395
A distal part of a long and slender bone shows some resemblance to the
metacarpal I11 of Deinonychus and is identified as third metacarpal faute de
mieux. Its distal end is expanded transversely and vertically, and the medial and
lateral margins of the articular surface are separated by a shallow groove. The
articular surface is not as rounded as in the corresponding element in
Driizony ckirs.
All phalanges show well-defined and highly finished surfaces for
interphalangeal articulation and deep, subcircular fossae (for attachment of
collateral ligaments) on each side of the distal articular ends.
Digit I is represented by the distal end of phalanx 1 and phalanx 2 (ungual).
The first phalanx shows a deeply grooved articular facet at its distal end, which
is only slightly asymmetrical. Thus, only slight rotation of the claw during
flexion occurred (as in Deinonychus; Osp-om, 1969: 105).
Digit I1 is known from the distal end of the penultimate phalanx (2) and
Phalanx 3 (ungual). The distal end of the second phalanx is deeply grooved,
markedly asymmetrical and slightly inclined with respect to the ridge on the
proximal articulation facet of the ungual, permitting supination of the claw
during flexion.
Digit 111 is documented by the distal part of phalanx 1, phalanx 3 (almost
complete) and phalanx 4 (ungual). The first phalanx is very short and srout and
has an asymmetrical distal facet. As in the corresponding phalanx of
Deinonychus, the condyles of the articular facet extend further back ventrally
than dorsally. The lateral condyle is larger than the median condyle and is less
rounded in lateral view. The penultimate phalanx is elongate. Obviously, the
third digit shows the same peculiar arrangement of phalanges as that described
in Deinonychus (Ostrom, 1969: 107).
The manus appears to be highly complex in its structure, well adapted to
powerful grasping, and might be regarded as a “miniature edition” of the
manus of Deinonychus (Fig. 4).
Most of the corresponding elements of the manus of Stenonychosaurus are
unknown. A manus claw figured by Russell (1969, fig. 1OD) is too incomplete
to warrant comparison. Sternberg (1932, pl. 2, fig. 2) figured the distal end of
phalanx 2 of digit I1 (now apparently lost), which resembles the corresponding
element in Saurornitholestes in its structure.
TAXONOMIC DISCUSSION
There are several small to medium-sized Judithian theropods, to which
Saurornitholestes langstoni has been compared: Stenonychosaurus inequalis
Sternberg, 1932; Dromaeosaurus albertensis Matthew & Brown, 1922 and
Chirostenotes pergracilis Gilmore, 1924.
Stenonychosaurus inequalis is relatively well known from cranial and
postcranial material, thoroughly described by Russell (1969).
Drornaeosaurus albertensis, redescribed by Colbert & Russell (1969), is
known from the holotype, consisting of an incomplete skull, some hyoid bones
and a few scattered bones of the left pes (AMNH 5356); furthermore, a left
frontal (NMC 12349) and a few pedal unguals can be referred to this species.
Chirostenotes pergracilis is based on associated left and right manus
(NMC 2367); Gilmore (1924) refers two extremely long and slender dentaries,
396
11:I).
SUES
Figure 5. Saurornitholestes langstoni, sp. nov. Holotype, left manus (reconstructed; preserved
parts shaded, proportions from Deinonychus and Velociraptor).
obtained from a different locality three years after the discovery of the
holotype, to Chirostenotes-a procedure not substantiated by any evidence.
Perhaps these dentaries belong t o the same taxon as an elongate frontal
(NMC 1 2 3 5 5 ) .
Comparison is restricted to frontals, teeth and phalanges of the manus,
although not even all of these elements are known for all three species.
The frontal of Saurornitholestes shows resemblance to that of
Stenorzychosaurus in its general outline and its relationships t o the surrounding
THEROPOD DINOSAUR FROM ALBERTA
399
differs in being relatively more elongate. I t differs from the frontal of
Saurornitholestes in the same features as does Stenonychosarairs (see Plate 8 ) .
The teeth of Saurornitholestes are different from those of Dromaeosazirzis
and Sarirornitlioides, a genus very closely related (if not identical) to
StenoYz?icIzosatirus, as already shown above. Direct comparison with
Steiz~~i~?~clzosatirzts
is not possible due to the lack of teeth definitely referable to
Stenon~~c1~0~airrrrs.
None of the two types of small theropod teeth from the
Judith River Formation, which are possibly referable t o Stenonychosuurzis
(Sues, 1977), is similar t o the teeth of Saurornitholestes.
The unguals are not strikingly different from those of any other
dromaeosaurid or saurornithoidid described. Only the enigmatic Chirostenotes
(a genus of problematical affinities) differs in having longer and less recurved
claws, a less prominent flexor tubercle and in lacking a secant cutting ventral
edge of the unguals; a characteristic feature is the presence of a prominent
dorsoposterior extensor crest (Gilmore, 1924; pers. obs. on P67.19.147; D. A.
Russell, in litt.).
Considering the differences to other Judithian theropods of similar size
presently known, which are ruling out reference of the new specimen to any
previously described genus, I have taken the approach t o consider it to
represent a new genus.
On the basis of its similarity t o Stenoiz),cliosazirzis in several features of the
frontal I originally referred this genus to the Saurornithoididae. However,
Saurornitholestes resembles Dromaeosaurtis in the shape of the endocranial
cavity, and the structure of the teeth of Saurornitholestes approaches the
dromaeosaurid pattern more closely than the saurornithoidid pattern,
supporting assignment to the Dromaeosauridae.
Ostrom (1969 and in litt.) only recognizes one family Dromaeosauridae
within the “deinonychosaurian” theropods, distinguished from all other small
to medium-sized theropods by the possession of the highly specialized second
digit of the pes. Various differences in the skull and pes (Russell, 1969;
Barsbold, 1974) support a distinction of Saurornithoides and Stenonychosa~iriison one hand and Deinonyclius, Dromaeosaunis and Velociraptor on
the other at the suprageneric level, at least at the level of subfamilies (a solution
which would be accepted by Ostrom (in litt.) to express the differences
between the two groups). I maintain a separation at the family level, as
proposed by Russell (1969 (“Troodontidae”) and in litt.) and Barsbold (1974).
However, the main difference between the Dromaeosauridae and
Saurornithoididae, as conceived by Barsbold (1974), is the presence of strongly
elongated prezygapophyses and chevrons provided with rod-like ossified
tendons in the tail of the genera referred t o the former family (Deinon~~clzrcs,
see Ostrom (1969: 60-80, figs 35-37); Velociraptor, see Kielan-Jaworowska &
Barsbold (1972: pl. 2, fig. 2)). The absence of these structures in the tail of the
holotype specimen of Saurornithoides junior is probably only an artifact of
preservation (Ostrom, in litt.); examination of Barsbold’s illustrations of the
caudal vertebrae (Barsbold, 1974: pl. 4, fig. 3b, c) reveals that the chevrons are
dorsoventrally compressed as in Deinonychs and Velociraptor and that this
feature already occurs on the 11th caudal vertebra - unlike nondeinonychosaurian theropods (Ostrom, in litt.) but as in Deinonychus and
Velociraptor.
I00
H.-D. SUES
Suurornithofestes is referred t o the Dromaeosauridae in this paper but
hrther material of the skull and pes might favor assignment to the
Saurornithoididae.
At least two dromaeosaurid genera are now reasonably well documented
from the Upper Cretaceous of North America.
ACKNOWLEDGEMENTS
I am especially grateful t o Mrs Irene Vanderloh for presenting her find t o the
Provincial Museum and Archives of Alberta and to Dr J . E. Storer, then at that
institution, who kindly put the specimen at my disposal.
Drs E. S. Gaffney, of the American Museum of Natural History, and D. A.
Russell, of the National Museum of Natural Sciences, permitted the loan of
material from their collections.
I profited greatly through discussions with Drs R. C. Fox, J . H. Ostrom and
D. A. Russell and I gratefully acknowledge their counsel and encouragement.
They also read a draft of the manuscript.
The photographs were skillfully prepared by Mr L. A. Lindoe. Illustrations
were prepared by the author.
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